Certain industrial automation controllers utilize a high-speed microprocessor (processor) and other components that generate heat beyond that which can be dissipated sufficiently using natural convection airflow. In such cases, the controller must utilize a fan to flow forced air through the controller housing in which the processor is located to cool the processor.
Use of a fan to cool an industrial automation controller has drawbacks including fan reliability and the tendency of the fan to draw contaminants into the controller housing including dust, dirt, moisture, corrosive particles, and other undesired particulates and contaminants that can damage the controller and degrade its performance over time and lead to a shorter operational life.
It is not unusual for industrial electronic devices to be used in environments with abnormally high levels of atmospheric contaminants. Printed circuit boards and their electronic components subjected to such atmospheres are often subject to shorter operational life because the contaminants may cause corrosion, short circuits, open circuits, unintended changes in impedances, etc. A device which requires forced convection for adequate cooling will expose the printed circuit board assembly (PCBA) to orders of magnitude greater airflow and atmospheric contaminants than a device which requires only natural convection for equivalent cooling.
The method typically used to solve this problem is conformal coating which adds a layer of protective material over sensitive areas of the printed circuit board and selected components. Challenges of employing conformal coating include: high cost due to material usage/process time/inspection/rework, difficulty in achieving complete coverage, difficulty in not applying material to areas like contacts or mating connectors, and difficulty in repairing PCBAs after coating. Designing for a more robust conformal coating process outcome typically results in inefficient use of printed circuit board (PCB) real estate (i.e. a larger product than desired or otherwise possible).
In certain known arrangements, a heat sink is attached to the processor or other heat-generating components on the PCBA to aid in cooling the device to which the heat sink is attached. Maintaining expected levels of reliability in a compact size requires an effective cooling interface between the processor and a heat sink without adding undue stress to processor solder joints or other components on a densely populated PCBA in an industrial environment wherein the PCBA is subjected to vibration, mechanical shock, and other harsh conditions. Known systems have been suboptimal in terms of providing an effective interface between the heat sink and processor or other component on the PCBA, without over stressing the solder joints and other portions of the PCBA.